The present invention relates to pressure gages in general, and more particularly to improvements in spring-loaded differential pressure gages.
It is known to employ in spring-loaded differential pressure gages a glass cylinder for steel piston which is reciprocable in and divides the interior of the cylinder into a high-pressure chamber and low-pressure chamber. The piston is biased by a compression spring in a direction to reduce the volume of the higher-pressure chamber. A drawback of such pressure gages is that the errors in readings are quite pronounced, e.g., in the range of .+-.0.035 atmosphere. Therefore these gages cannot be used for testing highly sensitive equipment, such as the pressure drop between the intake and discharge ends of filter elements and/or water separating elements in systems which are used for admission of fuel into the tanks of aircraft or the like. As a rule, the pressure differential between the intake and discharge ends of the aforementioned elements is less than 0.035 atmosphere. Such systems embody a host of safety features which are prescribed by authorities in order to insure that the tanks are filled with acceptable fuel.